Two secularist opposition parties in Turkey are joining forces to challenge the Islamist-rooted ruling AK Party in the July general election.
Turks have staged mass rallies in defence of secularism
The alliance was announced at a news conference on Thursday by the Republican People's Party (CHP) and Democratic Left Party (DSP).
The 22 July election was brought forward from November to try to resolve a dispute over the Turkish presidency.
Secularists accuse the AKP of trying to pursue an Islamist agenda.
Opinion polls indicate the AKP is still Turkey's most popular party.
Several giant opposition rallies have been staged in Turkish cities in defence of the country's secular institutions.
"We have agreed to form an election alliance. We will work together hand in hand," said CHP leader Deniz Baykal.
Opposition politicians want to weaken the AKP's control of the next parliament and prevent it imposing its candidate for president again.
The AKP withdrew its candidate - Foreign Minister Abdullah Gul - after a vote in parliament was rendered invalid by an opposition boycott.